Diaphony
Medieval term for early forms of polyphony (organum); originally Greek for discord or dissonance.
What it means
The word diaphony comes from Greek and originally meant discord or harsh sound, the opposite of symphonia, the pleasant blending of sounds. In this older sense, diaphonia or diaphonesis referred to a dissonant interval, a sound perceived as impure or tension-filled.
In the Latin Middle Ages the term shifted meaning and became a standard label for early forms of polyphony, especially organum, in which a second voice was added to a given liturgical melody (the cantus firmus) at fixed interval distances, often fourths or fifths. These early polyphonic practices, although by then regarded as a regulated musical technique, were still described with a word that had originally denoted dissonance, since the simultaneous sounding of two independent voices seemed unfamiliar and foreign from the perspective of the older monophonic tradition.
Musical use
In medieval treatises, diaphony frequently appears as synonymous with organum and serves as an umbrella term for the earliest notated forms of polyphonic church music, as described among others in the Musica enchiriadis (ninth century) and later organum treatises. Historically, diaphony marks a decisive step from monophonic chant toward medieval polyphony, out of which more complex techniques such as melismatic organum and eventually the motet later developed.
The ambiguity of the term matters: in antiquity, diaphonia meant dissonance in today's sense, while in the Middle Ages it denoted a regulated polyphonic technique that, from a modern standpoint, would generally be considered consonant. This shift in meaning reflects how the evaluation of simultaneous sounds changed over the centuries.